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CHRISTIAN-ALBRECHTS-UNIVERSITAT
Institut fur Anorganische Chemie
Prof. Dr. Norbert Stock
Kiel, 15.02.2016
Report on the doctoral thesis
"Coordination polymers based on pfiosptionic acids design, synthesis
and structural
characterization
prepared by Magdalena W i l k - K o z u b e k
Coordination polymers (CPs) are c o m p o u n d s c o m p o s e d of metal ions or clusters that are
connected in one, two or three dimensions by ligands. Especially crystalline C P s have
been in the focus of m a n y investigation since the systematic variation of metal ions and
linker molecules open up the possibility to change the structure and properties of these
compounds. Most impressive results have been reported for a subclass of C P s the metalorganic frameworks ( M O F s ) , which are CPs with potential porosity. T h e connection of
well-defined inorganic building units (IBUs, often also called s e c o n d a r y building units) by
rigid organic molecules, like aryl dicarboxylates, leads to three d i m e n s i o n a l f r a m e w o r k s .
The pore size as well as the pore surface chemistry can be t u n e d by using organic linker
molecules of different sizes and functionalized linker m o l e c u l e s . T h e "predictability" of the
final structures is mainly due to the fact that the carboxylate g r o u p s are restricted in their
coordination m o d e s . Hence t h e chemistry of metal carboxylate C P s is very well d e v e l oped.
Organic linker molecules containing other functional g r o u p s such a s - G e ( 0 H ) 3 , -PO3H2
or -SO3H have been less frequently e m p l o y e d in the synthesis of C P s . This is due to the
fact that the larger n u m b e r of coordinating 0 - a t o m s at e a c h functional group leads to a
larger structural variability. Hence, different predictable IBUs are only rarely observed and
thus the tuning of CP structures is not possible. Nevertheless the use of linker molecules
containing -PO3H2 g r o u p s is of special interest in the synthesis of C P s since there exists
a large number of synthetic routes to obtain (poly)phosphonic acids. In addition, metal
phosphonates are often chemically and thermally more stable c o m p a r e d to metal carboxylates, which is due to the higher charge of the fully d e p r o t o n a t e d g r o u p (-P03^" vs -COO"
) as well as the larger n u m b e r of coordinating 0 - a t o m s .
1
The dissertation of Ms W i l k - K o z u b e k deals with the topic of metal phosphonate CPs. T h e
synthesis of phosphonic acids containing different n u m b e r s of -PO3H2 groups or additional functional groups such as - C O O H , NO2 or pyridyl units, and their detailed characterization as well as their use in the synthesis of new metal phosphate coordination polymers is reported. All c o m p o u n d s were characterized in great detail mainly using spectroscopic as well as X-ray diffraction methods and the crystal structures w e r e topologically
analyzed.
In the introduction (Chapter 1) the topic of the dissertation is very well introduced. T h e
definitions are s u m m a r i z e d and the most important synthesis m e t h o d s of phosphonic acids and metal p h o s p h o n a t e s are presented.
After the objectives of the work are shortly s u m m a r i z e d in Chapter 2, the syntheses of
the c o m p o u n d s and their characterization is covered in C h a p t e r 3. T h e phosphonic acids
(4-nitrophenyl)methylphosphonic acid
(H2LI), (4-phosphonomethyl)benzoic acid (H3L2)
as well as the p s e u d o p o l y m o r p h s H2LO.5C4H8O2, 2 H 2 L C 2 H 5 O H and H2LH2O, 1,2-phenylenbis(methylphosphonic
H4L3,
acid)
1,2,4,5-benzenetetrayltetrakis
(methylphosphonic) acid (H8L4), 3-pyidinylphosphonic acid
(H2L6), 5-phosphono-3-pyri-
dinecarboxylic acid (HsL?) and 3,5-pyridinediylbisphosphonic acid
(H4L8) were obtained
and characterized by ^H-, ^^P{^H}-NMR spectroscopy to confirm phase purity. R o o m t e m perature crystal growth experiments resulted in crystals that w e r e suitable for structure
determination by single-crystal X-ray diffraction.
The phosphonic acids w e r e e m p l o y e d in the synthesis of C P s using Co-, Z n - , C d - and
Ca-salts. R o o m temperature synthesis (slow evaporation of the solvent) as well as solvothermal reactions employing autoclaves were carried out to obtain single crystals.
These
investigations
led
to
the
compounds
[Co(H2L2)2(H20)4],
[Co(4,4'-
bpy)(H2O)4]-2H2L20.188(0), [Co(H20)6][H(H2L5)2]2-2H20, [ M ( L 6 ) ( H 2 0 ) 5 ] (with M = M n ,
Co),
[ZnCI(HL6)]n,
[C02(L7)(H2L7)(H20)3]n,
[Ca(H3L8)2(H20)]n,
[Co(H20)6][Co(L8)(H20)5]-5(0) and [M(H3L8)2(H20)2]n (with M = C o , Z n , Cd). S o m e t i m e s
only minute a m o u n t s of the c o m p o u n d s were obtained and further characterization could
not be carried out for these c o m p o u n d s . In the other cases they w e r e analyzed regarding
the elemental composition, and the simulated P X R D patterns w e r e c o m p a r e d to the experimental ones. In addition, the thermal stabilities w e r e d e t e r m i n e d by thermogravimetric
measurements and the IR/Raman spectra w e r e recorded and interpreted.
2
The results of the structure determinations and the results of the characterization m e a s urements of the phosphonic acids and the metal p h o s p h o n a t e s are presented in Chapter
4. This chapter starts off with a s u m m a r y of coordination m o d e s that have been observed
in metal phosphonates a n d a list of c o m p o u n d s ( C S D reference codes) that have been
obtained in previous studies w h e n the phosphonic acid derivatives of this thesis were
employed. Subsequently the results of the structure determinations are presented in great
detail taking into account coordination environments, hydrogen bonding and P = 0 n interactions. T h e intermolecular interactions of the phosphonic acid molecules in t h e crystal
structures were determined by Hirshfeld surface analysis.
Due to the large n u m b e r of crystal structures certain conclusion w e r e d r a w n , which c o n firm trends observed in previous studies. Thus, in most of the c o m p o u n d s the metal ions
are octahedrally s u r r o u n d e d , the exception being Zn^^, w h i c h has a tetrahedral coordination environment in [ZnCI(HL6)]n. Different coordination m o d e s w e r e observed for the
phosphonate groups a n d the carboxyl and carboxylate g r o u p s w e r e involved in h y d r o g e n bonding interactions. In contrast to Ca^"" which w a s only s u r r o u n d e d by 0 - a t o m s , in the
c o m p o u n d s containing Mn^"", Co^"^ a n d Zn^"" ions coordination of the N-atoms w a s also
observed. Counter ions a n d solvent molecules either complete t h e coordination sphere
of the metal ions or occupy space in the structure a n d both are involved in hydrogen
bonding.
The thesis of M s W i l k - K o z u b e k is very well written. It is a very systematic work that i n volves synthesis and characterization at a high scientific level. T h e data is of high quality
and presented accordingly. T h e results have been s u m m a r i z e d in s e v e n publications in
different pre-reviewed international journals. In addition, they have been presented at
various conferences mainly as poster presentations, but also as oral presentations. Nevertheless there are also s o m e part that could be further i m p r o v e d . T h u s additional m e a s urements for e x a m p l e , t e m p e r a t u r e dependent P X R D investigations or the determination
of proton conductivity would have been very interesting. Discussion a n d comparison to
literature data could also be improved in order to set the newly obtained results in a better
context. Taking all these points into account the thesis definitely fulfills the requirements
for receiving a P h D in Chemistry. It w a s a pleasure reading t h e thesis a n d learning more
about metal p h o s p h o n a t e s .
der Christian-A!bre3hts-Universitat zu Kiel
Max-Eyth-StraBe2, D-24118 Kiel